JPH10124902A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assure a signal intensity level at a sufficiently high level by using the light beams of light sources which emit the light beams of the wavelengths which are absorbed to a lesser degree by dyestuff at the time of reproducing a recording medium formed with a recording film by using the dyestuff. SOLUTION: The disk formed with the recording film by using the dyestuff is reproduced by using the laser beams(LBs) from first and second semiconductor lasers 1, 2 on long and short wavelength sides. The absorption of the LBs by the dyestuff of the recording film is large with the LB from the laser 2 at present but is larger with the LB from the laser 1 in some cases from the relation with the material quality of the dyestuff of the recording film. In such a case, both of the second pupil part 10 of a pupil filter 7 and the filter surface 5 of a beam splitter 4 are formed by a wavelength selective dichroic filter. As a result, the sufficient signal intensity level is obtd. by selectively switching the third pupil different in the diameter from the diameter of the first and second pupil parts 9, 10 by using the LB from the laser 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading signals from both a normal density recording medium and a high density recording medium having different recording densities, and more particularly, to a recording medium having a recording film formed using a dye. The present invention relates to an optical pickup device that takes into account reproduction of data.

[0002]

2. Description of the Related Art As an optical disk in which a signal is optically read using a light beam such as a laser beam,
CDs (Compact Disks) have become widespread, but high-density disks that have been standardized in order to increase the capacity while ensuring compatibility with the same disk diameter as the CDs in response to the need for even larger capacities have been developed. Proposed.

This high-density disk uses a short wavelength semiconductor laser and uses an optical pickup device with a high resolution optical system to read a signal recorded at a higher density than a CD.

In order to make the optical pickup device capable of reading signals from both a CD and a high-density disk, a semiconductor laser having a short wavelength is used, and a pupil diameter for limiting a laser beam incident on an objective lens is read from the disk. A method is known in which the NA value is adapted to the signal recording density of the disc by switching according to the signal recording density as an objective lens. This optical pickup device reduces the pupil diameter when reading a CD to reduce the objective lens. In reading a high-density disc, the pupil diameter is increased to increase the NA value of the objective lens when reading a high-density disc, thereby supporting both CD and high-density disc signal reading.

[0005]

Meanwhile, in a CD-R disk (write-once compact disk), a signal pit is formed by decomposing a dye on a recording film for recording a signal, and the signal is read by a change in the reflectance of a laser beam. Is performed. Therefore, an optical pickup device in a disc device capable of reproducing a CD-R disc is a CD-R disc.
Although it is necessary to detect the change in the reflectance of the recording film of the -R disc, as described above, when a short-wavelength semiconductor laser is used to read signals from both a CD and a high-density disc, the CD-R It is said that the absorption of the laser beam increases due to the dye in the recording film of the disc, and the signal intensity level obtained by the optical pickup device decreases to about 1/5 to 1/10 depending on the wavelength of the laser beam of the semiconductor laser. A phenomenon occurred, and a situation occurred in which reading of a CD-R disc could not be performed.

As described above, in order to switch the pupil diameter for limiting the light beam incident on the objective lens according to the signal recording density, a mechanism for mechanically moving the two pupils and a shutter are opened and closed. If a mechanism is required, or if a liquid crystal shutter is used, electrical wiring is required, resulting in a structure that is difficult to manufacture.

[0007]

SUMMARY OF THE INVENTION The present invention comprises a first and a second light source for emitting light beams having different wavelengths from each other, and a recording film for reproducing a recording medium on which a recording film is formed using a dye. By using a light beam of a light source that emits a light beam having a wavelength that is less absorbed by the dye, a sufficient signal intensity level obtained by the optical pickup device is ensured.

A single light source including a first light source for emitting a light beam having a wavelength suitable for a high-density recording medium and a second light source for emitting a light beam having a wavelength suitable for a high-density recording medium is provided. Signals are read from two types of recording media having different recording densities depending on the pickup device. In this case, a pupil filter for restricting a light beam from the first light source and the second light source incident on the objective lens, and a first pupil portion transmitting the light beams of the first and second light sources to the pupil filter And reflecting a light beam having a diameter larger than that of the first pupil portion and having a wavelength of the first light source,
Forming a second pupil portion comprising a wavelength selection filter that transmits a light beam having the wavelength of the second light source, thereby limiting the light beam from the first light source by the pupil diameter of the first pupil portion; The light beam from the second light source is limited by the pupil diameter of the second pupil. By doing so, it is possible to switch the NA value of the objective lens without a mechanical drive unit or electrical wiring.

[0009] A first light source is provided such that the polarization directions of the light beams incident on the objective lens are different from each other by approximately 90 degrees.
And a pupil filter for limiting a light beam from the first light source and the second light source incident on the objective lens. A first pupil portion for transmitting the light beams of the first and second light sources to the pupil filter; and a diameter larger than the first pupil portion and perpendicular to the polarization direction of the light beam of the first light source, and Limiting the light beam from the first light source by the pupil diameter of the first pupil portion by forming a second pupil portion comprising a polarization filter having a polarization direction parallel to the polarization direction of the light beam of the second light source. At the same time, the light beam from the second light source is limited by the pupil diameter of the second pupil portion. By doing so, it is possible to switch the NA value of the objective lens without a mechanical drive unit or electrical wiring.

A beam splitter arranged on the optical path of the light beam modulated by the recording medium is constituted by a filter surface so that one of the first and second light sources is reflected by the filter surface. At the same time, the other light beams of the first and second light sources are transmitted.
With this configuration, the light beams of the first and second light sources are efficiently branched into different optical paths without loss, and a photodetector is disposed in each of the branched optical paths to form the light beam. The respective light beams of the first and second light sources are respectively received by dedicated photodetectors.
Here, when the wavelengths of the respective light beams of the first and second light sources are different, this is achieved by configuring the filter surface with a wavelength selection filter.
In the case where the first and second light sources are arranged so that the polarization directions of the respective light beams incident on the objective lens of the light source are substantially different from each other, it may be achieved by configuring the filter surface with a polarizing filter. good.

[0011]

FIG. 1 is an arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention. The optical pickup device shown in FIG. 1 is a normal density recording disk of the CD family and a DVD (digital video disk). Of a high-density recording disk.

In FIG. 1, reference numeral 1 denotes a first semiconductor laser which emits a laser beam having a wavelength suitable for a normal density recording disk, for example, 780 nm. Reference numeral 2 denotes a laser beam having a wavelength suitable for a high density recording disk, for example, 635 nm. A second semiconductor laser that emits light. The laser beam emitted from the first semiconductor laser 1 is reflected by the first half mirror 3, and the reflected laser beam enters the beam splitter 4.

The beam splitter 4 is configured by providing a filter surface 5 on a prism.
It is formed of a wavelength-selective dichroic filter that reflects a laser beam of the wavelength of the semiconductor laser 1 and transmits a laser beam of the wavelength of the second semiconductor laser 2. The laser beam from the first semiconductor laser 1 incident on the beam splitter 4 is substantially totally reflected by the wavelength selection filter surface 5, converted into parallel light by the collimator lens 6, and then incident on the objective lens 8 by the pupil filter 7. The luminous flux is restricted and the objective lens 8
And is converged by the objective lens 8 on a signal surface (not shown) of the disk.

The pupil filter 7 includes a first semiconductor laser 1 and a second semiconductor laser 1 as shown in the plan view of FIG.
First pupil portion 9 opened to transmit
And reflects a laser beam having a diameter larger than that of the first pupil portion 9 concentric with the first pupil portion 9 and having a wavelength of the first semiconductor 1 and transmitting a laser beam having a wavelength of the second semiconductor laser 2. A second pupil portion 10 composed of a wavelength-selective filter (dichroic filter).

Therefore, the laser beam from the first semiconductor laser 1 is applied to the first pupil portion 9 of the pupil filter 7.
The light flux is limited by the diameter of the objective lens 8 and enters the objective lens 8.

The laser beam modulated and reflected by the signal surface of the disk returns to the objective lens 8 and is reflected by the filter surface 5 of the beam splitter 4 via the first pupil portion 9 of the pupil filter 7 and the collimator lens 6. After that, it is returned to the first half mirror 3. And
The laser beam transmitted through the first half mirror 3 is
The light is received by the photodetector 11.

That is, when a laser beam emitted from the first semiconductor laser 1 is used, the first photodetector 11 is used to receive a modulated beam of the laser beam modulated by the signal surface of the disk. And the first
The photodetector 11 can obtain various signals necessary for reproducing the recorded signal on the disk.

When a laser beam emitted from the first semiconductor laser 1 is used, the objective lens is set in accordance with the effective diameter of the objective lens 8 set by the diameter of the first pupil portion 9 of the pupil filter 7. 8, the light spot diameter and the focal depth converged on the signal surface of the disk can be determined based on the NA value and the wavelength of the laser beam emitted from the first semiconductor laser 1. Therefore, by setting the wavelength of the laser beam emitted from the first semiconductor laser 1 and the diameter of the first pupil portion 9 of the pupil filter 7 with respect to the objective lens 8, the light spot from which the recording signal of the disc is read can be adjusted to the normal density. The light spot diameter and the focal depth suitable for the recording disk can be set.

The laser beam emitted from the second semiconductor laser 2 is reflected by the second half mirror 12, and the reflected laser beam is incident on the beam splitter 4. The laser beam from the second semiconductor laser 2 incident on the beam splitter 4 is applied to a filter surface 5.
After being substantially transmitted through the collimator lens 6 and converted into parallel light by the collimator lens 6, the luminous flux incident on the objective lens 8 is restricted by the pupil filter 7 and is incident on the objective lens 8, and converges on the signal surface of the disk by the objective lens 8. Is done.

Here, the second pupil portion 10 of the pupil filter 7 is formed of a filter that transmits a laser beam having a wavelength emitted from the second semiconductor laser 2. Therefore, the laser beam from the second semiconductor laser 2 passes through the second pupil portion 10 of the pupil filter 7, and the luminous flux is limited by the diameter of the second pupil portion 10 and is incident on the objective lens 8. become.

The laser beam modulated and reflected by the signal surface of the disk returns to the objective lens 8 and passes through the second pupil portion 10 of the pupil filter 7 and the filter surface 5 of the beam splitter 4 via the collimator lens 6, Thereafter, the light is returned to the second half mirror 12. Then, the laser beam transmitted through the second half mirror 12 is received by the second photodetector 13.

That is, when a laser beam emitted from the second semiconductor laser 2 is used, the second photodetector 13 is used to receive a modulated beam of the laser beam modulated by the signal surface of the disk. And the second
The photodetector 13 can obtain various signals necessary for reproducing a recorded signal on the disk.

When the laser beam emitted from the second semiconductor laser 2 is used, the objective lens is set in accordance with the effective diameter of the objective lens 8 set by the diameter of the second pupil portion 10 of the pupil filter 7. 8 is determined, and the light spot diameter and the focal depth converged on the signal surface of the disc can be determined based on the NA value and the wavelength of the laser beam emitted from the second semiconductor laser 2. Therefore, by setting the wavelength of the laser beam emitted from the second semiconductor laser 2 and the diameter of the second pupil portion 10 of the pupil filter 7 with respect to the objective lens 8, the light spot from which the recording signal of the disk is read can be increased in density. The light spot diameter and the focal depth suitable for the recording disk can be set.

As described above, in the case of a normal density recording disk, the wavelength of the laser beam emitted from the first semiconductor laser 1 and the diameter of the first pupil portion 9 of the pupil filter 7 are set, whereby the high density recording disk can be obtained. In this case, by setting the wavelength of the laser beam emitted from the second semiconductor laser 2 and the diameter of the second pupil portion 10 of the pupil filter 7, the diameter of the light spot and the depth of focus can be set. The setting of the light spot diameter and the depth of focus can be performed independently for any disk with respect to the recording disk.

When a normal density recording disk (CD-R) on which a recording film is formed using a dye is reproduced, the light is emitted from the first semiconductor laser 1 because the normal density recording disk is reproduced. This laser beam has a wavelength that is much less likely to be absorbed by the dye of the recording film of the normal density recording disc than the laser beam from the second semiconductor laser 2.

Therefore, even in the case of a normal density recording disk on which a recording film is formed by using a dye, a change in the reflectance of the recording film of the disk is received by the first photodetector 11 at a sufficient light intensity level. And the first photodetector 1
By means of 1, various signals necessary for reproducing the recorded signal of the disc can be sufficiently obtained.

By the way, at present, as for a disk on which a recording film is formed by using a dye, a laser beam from the second semiconductor laser 2 on the short wavelength side is more easily absorbed by the dye of the recording film. Due to the material of the dye used, the laser beam from the second semiconductor laser 2 on the short wavelength side is more reduced in absorption of the recording film by the dye,
If the absorption of the laser beam from the first semiconductor laser 1 on the longer wavelength side is larger due to the dye on the recording film,
When reproducing such a disc, the second
The laser beam from the semiconductor laser 2 may be used. In this case, it is necessary to selectively switch and use a third pupil having a diameter different from that of the first pupil portion 9 and the second pupil portion 10 of the pupil filter 7 depending on the light spot diameter and the depth of focus to be set. is there.

In the embodiment, the second pupil portion 10 of the pupil filter 7 and the filter surface 5 of the beam splitter 4 are both formed by a wavelength-selective dichroic filter. If the semiconductor laser 2 and the semiconductor laser 2 are arranged so that the polarization directions of the light beams incident on the objective lens 8 are different from each other by approximately 90 degrees, the second pupil portion 10
Even if both the filter surface 5 of the beam splitter 4 and the filter surface 5 are formed by polarizing filters, the same function can be obtained.

[0029]

As described above, the present invention relates to a light source which emits a light beam having a wavelength which is less absorbed by a dye in a recording film when reproducing a recording medium having a recording film formed using the dye. Since the light beam is used, the signal intensity level obtained by the optical pickup device can be secured at a sufficient level, and various signals necessary for reproducing the recorded signal of the disc can be sufficiently obtained. I can do it.

The present invention also provides a first pupil portion for transmitting the light beams of the first and second light sources to a pupil filter for restricting a light beam from the first light source and the second light source incident on the objective lens; Forming a first pupil portion and a second pupil portion having a diameter larger than the first pupil portion and including a filter transmitting a predetermined one of the first light source and the second light source. Is limited by the pupil diameter of the first pupil portion, and the other light beam of the first light source and the second light source is limited by the pupil diameter of the second pupil portion. The NA value can be switched with a simple configuration without providing a pupil diameter switching mechanism.

According to the present invention, a beam splitter disposed on an optical path of a light beam modulated by a recording medium is constituted by a filter surface, and the filter surface is formed by first and second filter surfaces.
While making one light beam of the light source reflected,
Since the other light beams of the first and second light sources are transmitted, the light beams of the first and second light sources can be efficiently branched to different light paths without loss. A dedicated photodetector corresponding to each of the first and second light sources can be arranged in each of the branched optical paths. In this case, when the wavelengths respectively emitted from the first light source and the second light source are different, it can be achieved by configuring the filter surface with a wavelength selection filter. The polarization direction of each light beam incident on the lens is approximately 9
When the first and second light sources are arranged so as to be different from each other by 0 degrees, this can be achieved by configuring the filter surface with a polarizing filter, and the configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is an arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a plan view for explaining a pupil filter 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st semiconductor laser 2 2nd semiconductor laser 4 Beam splitter 5 Filter surface 7 Hitomi filter 8 Objective lens 9 1st pupil part 10 2nd pupil part 11 1st photodetector 13 2nd photodetector

Claims (5)

[Claims] 1. An optical pickup device capable of reading a signal on a recording medium having a recording film formed by using a dye, comprising: a first light source and a second light source that emit light beams having different wavelengths. An optical pickup device, wherein a light beam of a light source which emits a light beam having a wavelength smaller in absorption by a dye of a recording film when reproducing a medium is used. 2. An optical pickup device for reading signals from both a normal density recording medium and a high density recording medium having different recording densities, comprising: a first light source for emitting a light beam having a wavelength suitable for the normal density recording medium; A second light source for emitting a light beam having a wavelength suitable for a high-density recording medium, and an NA of an objective lens.
A pupil filter for limiting light beams from the first light source and the second light source incident on the objective lens for setting a value, wherein the pupil filter transmits a first light beam from the first and second light sources. A second pupil portion comprising a pupil portion and a wavelength selection filter which has a larger diameter than the first pupil portion and reflects a light beam having the wavelength of the first light source and transmits a light beam having the wavelength of the second light source. An optical pickup device comprising: 3. An optical pickup device for reading signals of both a normal density recording medium and a high density recording medium having different recording densities, wherein polarization directions of light beams incident on an objective lens are different from each other by approximately 90 degrees. And a pupil filter for limiting a light beam from the first light source and the second light source incident on the objective lens to set an NA value of the objective lens, the pupil comprising: The filter has a first pupil portion for transmitting the light beams of the first and second light sources, a diameter larger than that of the first pupil portion, perpendicular to a polarization direction of the light beam of the first light source, and a second light source. A second pupil portion comprising a polarizing filter having a polarization direction parallel to the polarization direction of the light beam. 4. A recording medium comprising a first light source for emitting a light beam having a wavelength suitable for a normal density recording medium and a second light source for emitting a light beam having a wavelength suitable for a high density recording medium, having different recording densities. What is claimed is: 1. An optical pickup device for reading signals of two types of recording media, comprising: a light beam of one wavelength of the first and second light sources; and a light beam of the other wavelength of the first and second light sources. A beam splitter having a wavelength selection filter surface that transmits light, and disposed on an optical path of a light beam modulated by a recording medium; and a first light beam disposed on an optical path of a light beam reflected by the wavelength selection filter surface. An optical pickup device comprising: a detector; and a second photodetector disposed on an optical path of a light beam transmitted through the wavelength selection filter surface. 5. An optical pickup device for reading signals of both a normal density recording medium and a high density recording medium having different recording densities, wherein polarization directions of light beams incident on an objective lens are different from each other by approximately 90 degrees. And a light source in one of the first and second light sources in a polarization direction, and a light beam in the other of the first and second light sources in the other polarization direction. A polarizing beam splitter disposed on the optical path of the light beam modulated by the recording medium, a first photodetector disposed on the optical path of the light beam reflected by the polarizing filter surface, An optical pickup device comprising: a second photodetector disposed on an optical path of a light beam transmitted through the polarizing filter surface.